1. Field of the Disclosure
This disclosure generally relates to a method of preparation of compositions of supported ionic catalyst systems that are useful for additions of olefinically unsaturated monomers, e.g., polymerization, wherein the catalyst system is synthesized from a novel supported activator. This disclosure is useful in coordination polymerization processes that utilize supported compounds as for gas phase or slurry polymerization of olefinically unsaturated monomers. This disclosure is useful for polymerization processes using the compositions. The catalyst compositions comprise: a) a metal oxide support; b) silyl-capping of this support in order to reduce the number of available surface hydroxyls; c) formation of a silica-bound anion derived from this silylated support; and d) activation of a metallocene or olefin polymerization precursor catalyst.
2. Detailed Description of the Prior Art
Coordination polymerization of olefinically unsaturated monomers is well known and has led to a proliferation of elastomeric and plastic compositions of matter, such as polyethylene, polypropylene and ethylene/propylene copolymers. The early work utilized transition metal compounds with such activators as aluminum alkyls. Later work extended this to bulky transition metals (“metallocenes”) (e.g., η5-cyclopentadienyl) with such activators as alkyl alumoxanes. More recent developments have shown the effectiveness of ionic catalysts comprised of metallocene cation activated by non-coordinating anions. Group 13 based Lewis acids having fluorinated aryl substitutents are known to be capable of activating transition metal compounds into olefin polymerization catalysts. Trisperfluorophenylborane, for example, is capable of ionizing cyclopentadienyl derivatives of transition metals by abstracting a ligand and providing a stabilizing, compatible non-coordinating anion. The term “non-coordinating anion” is accepted terminology in the field of olefinic polymerization, both by coordination or insertion polymerization and carbocationic polymerization. The non-coordinating anions are described to function as electronic stabilizing co-catalysts, or counterions, for cationic metallocene complexes that are active for olefin polymerization. Non-coordinating anions as used herein applied both to non-coordinating anions and to coordinating anions that are at most weakly coordinated to the cationic complexes so as to be labile to replacement by unsaturated monomers such as olefinically or acetylenically unsaturated monomers. The use of ionic catalysts for polymerization of unsaturated monomers where organometallic transition metal cations are stabilized in an active polymerization state by compatible, non-coordinating anions is a well-recognized field in the chemical industry. Typically, such organometallic transition metal cations are the chemical derivatives of organometallic transition metal compounds having both ancillary ligands to help stabilize the compound in an active electropositive state and labile ligands including at least one of which that can be abstracted to render the compound cationic and at least one of which that is suitable for olefin insertion. Inert supports are industrially employed for insertion polymerization processes in both slurry and gas phase polymerization, technology for supporting these ionic catalysts is also known.
The chemical bonding of non-coordinating anionic activators to supports so as to prepare polyanionic activators that when used with the metallocene precursor compounds avoid problems of catalyst desorption experience when ionic catalysts physically adsorbed on metal oxide supports are utilized in slurry or solution polymerizations. Detailed description of silica-bound anion technology is discussed in U.S. Pat. No. 5,643,847 and is incorporated herein by reference.
Accordingly, the preparation of supported polymerization catalyst systems in many instances requires the control of the number of available surface hydroxyl groups. A conventional means of reducing the number of surface hydroxyls is to heat the silica support in an inert atmosphere to an elevated temperature (600° C. for example), chosen based on the degree of dehydroxylation desired, hence, reducing the number of available hydroxyl groups for subsequent reactions. At times thermal dehydroxylation is utilized in conjunction with additional methods of reducing available hydroxyl groups. For example, one means of further reducing the number of hydroxyl groups is to fluoride the support by means of a conventional fluoriding agent, in order to adjust the hydroxyl count into the desired range. Fluoriding of metal oxide supports is a well known technique to those skilled in the art. Other means of effectively reducing the availability of surface hydroxyls are known in the literature (Vansant, E. F.; Van Der Voort, P.; and Vrancken, K. C. “Characterization and Chemical Modification of the Silica Surface”. Elsevier Science B. V., 1995). These surface modifications can be costly or not practical from a catalyst scale-up perspective.
There is a continuing need for improvements in the method of preparation of effective polymerization catalysts of the type described above. In particular there is a need for procedures with fewer steps and with more control of the stoichiometry such that an optimum number of surface hydroxyl groups are made available for conversion to a silica-bound anion.
The present disclosure employs an alternative route to efficiently decrease the number of surface hydroxyl groups, thus avoiding the use of a costly fluoriding step, described by Piers, W. E. et al., in the Journal of Organic Chemistry 1999, 64, 4887, which is incorporated herein by reference. Importantly, the present disclosure provides for a practical one-pot synthesis of the final catalyst formulation by conducting the silane capping (hydroxyl reduction), activator formation and catalyst activation in one pot. The present inventors have developed a novel process whereby the fluoriding step can be eliminated and wherein dehydroxylating can take place at the reduced temperatures, thus resulting in substantial energy savings as well.